Oh, I've been known to say 'That valve (tube) is white round the top. Somebody has let the vacuum out' Seems like quite a reasonable way of putting it :-) Try explaining how important a tight vacuum system on a mass spectrometer is to some PHD chemists. Not to mention how to find the leaks. It is amazing how little they teach in "leading" colleges today. Definately NO common sense. So often all the problem consists of is the last thing they worked on but did that enter their mind? Dan